Two different types of human mast cells have been identified and distinguished from basophils based primarily on the neutral protease composition of their secretory granules. The MCrc type of mast cell contains tryptase, chymase, cathepsin 6-like protease and mast cell carboxypeptidase; the MCr type contains only tryptase; and basophils contain negligible to undetectable amounts of these proteases. Each cell type also exhibits special ultrastructural features and distributions within their host. Aim 1 will investigate the special constituents of human mast cells and basophils. The proteoglycan type(s) will be determined along with the expression of tryptase and chymase protein and mRNA in different types of human mast cells and basophils. We expect to determine whether mature and developing MCt and MCrc cells contain the same proteoglycan species, whether these mast cell subtypes differ in chymase mRNA content, like protein content, and whether in situ hybridization for tryptase or chymase mRNA identifies committed mast cell progenitors prior to protein expression and distinguishes activated from resting mast cells, and to clone and sequence an apparently unique constituent of human basophils. Aim 2 will examine the growth, differentiation and survival of different types of human mast cells and basophils. These studies are based in part on the important new finding that stem cell factor (Kit ligand) is a major growth factor for human mast cells. Initially the focus will be on IL-4, interferons alpha and gamma and various steroids. Effects on FcepsilonRI and Kit expression, on proteases and histamine, and selectivity for MCt cells, MCrc cells and basophils will be studied. Finally, the capacity of murine and human fibroblasts to complete the maturation of stem cell factor-dependent mast cells will be examined. Aim 3 will determine the involvement of different types of human mast cells and basophils in human diseases, using techniques developed in previous aims. Also, a means by which mast cell progenitor frequency in the peripheral blood can be assessed will be devised and used to analyze peripheral blood patients with diseases with mast cell hyperplasia (systemic mastocytosis), depletion (AIDS) and activation (allergic rhinitis). Better characterization of mast cells and basophils will provide more precise means to measure and monitor. their involvement in human disease, and better strategies for therapeutic interventions.